If you are to start share buying it makes sense to first get the answer to the question, what are shares?
Ordinary shares give the holder the right to claim a share of ownership of the business. If you held all the ordinary shares you would own the company outright and then you will be the only person that the managers of the business are answerable to. You can sack them if you want to. If you hold a small proportion then you have to share the rights of ownership, such as deciding on the team of directors or the size of dividends, with other shareholders. When there are many shareholders companies use voting mechanisms to find out what the majority of shareholders want to happen.